It is well known that regulating the exposure of oxygen-sensitive products to oxygen maintains and enhances the quality and "shelf-life" of the product. For instance, by limiting the oxygen exposure of oxygen sensitive food products in a packaging system, the quality of the food product is maintained, and food spoilage is avoided. In addition such packaging also keeps the product in inventory longer, thereby reducing costs incurred from waste and having to restock inventory. In the food packaging industry, one means for regulating oxygen exposure that has been developed uses polymeric films made from the oxygen scavengers disclosed in U.S. Pat. No. 5,346,644 issued to Speer et al Sep. 13, 1994, and in copending U.S. Ser. No. 276,125 filed Jul. 15, 1994 for "Compositions, Articles and Methods for Scavenging Oxygen". A method of initiating oxygen scavenging generally is disclosed in U.S. Pat. No. 5,211,875 issued to Speer et al. May 18, 1993, and in U.S. Ser. No. 263,596 filed Jun. 22, 1994. The references are incorporated herein by reference as if set forth in full. These oxygen scavengers have a demonstrable effect on the quality of certain food products. Further, these materials can be used as a lidstock or incorporated in multilayer packaging materials to produce thin, flexible, transparent films that are high oxygen barriers, or are capable of scavenging oxygen from the headspace of a package. These films are an effective substitute for a 15-40 micrometer layer of aluminum foil in some applications.
It has been found that the oxygen scavenging process may produce by-products such as organic acids or aldehydes that can result in off-odors and flavors. Migration of these by-products is not necessarily prevented by the presence of layers which are fairly effective barriers to other materials such as gaseous oxygen or carbon dioxide. However, if a layer containing an additive that reacts readily with oxidation by-products is employed in a multilayer package, the occurrence of off-odors or flavors that result from the oxygen scavenging process can be either reduced or prevented.
Various means of regulating off-odors and flavors in polymeric materials are known. For example, U.S. Pat. No. 5,340,884, issued to Mills et al. Aug. 23, 1994, relates to the use of polyester blended with low molecular weight polyamides instead of pure polyester to produce a high barrier resin with a reduced amount of residual acetaldehyde.
U.S. Pat. No. 4,908,151, issued to Inoue Mar. 13, 1990, teaches that an oxygen absorbent sachet can be made using a liquid unsaturated fatty acid, a transition metal, preferably iron, and a base. The base is disclosed to solidify the liquid unsaturated fatty acid and reduce odors caused by the reaction of the fatty acid with oxygen. The disclosure is directed to maximizing the available surface area of the acid, thereby enhancing its reactivity (Col. 8, lines 43-49). There is no indication that a useful oxygen absorbent can be formed into films and need not be separately packaged in a sachet.
Aldehyde-absorbing layers made of polyalkylene imines are known for incorporation into polyethylene and polypropylene films as a method of reducing the build-up of oil degradation by-products from snack foods, see U.S. Pat. No. 5,284,892 issued to Brodie et al., Feb. 8, 1994, for "Aldehyde Scavenging Compositions and Methods Relating Thereto" and in protective clothing as a barrier layer, see U.S. Pat. No. 5,391,426 issued to Wu Feb. 21, 1995. However, there has been no indication that incorporation of these materials in a multi-layer packaging film will be effective to reduce migration of the by-products of oxygen absorption that takes place within an ethylenically unsaturated film layer.
European Patent Publication 504 276 A1 discloses that cyclic urea derivatives can be incorporated in a sachet with an oxygen absorbent and an ethanol source. The cyclic urea derivative absorbs acetaldehyde produced by the oxidation of ethanol. The oxygen absorber is preferably iron filings or a zeolite powder. Neither polymeric oxygen scavengers nor the making of films is disclosed or discussed.
Japanese Kokai Patent No. HEI 5-247276 published Sep. 24, 1993 by Toppan Printing Co. discloses odor suppression in an oxygen barrier film by blending a variety of adsorbents into a monolayer film made of an oxygen scavenging resin. The reference discloses a wide variety of resins. All the experiments are directed to the combination of "natural zeolite" with polyethylenes and polypropylenes, which are different from the preferred oxygen scavengers used in the present invention, and which are acknowledged to degrade upon oxidation (page 6, lines 7-12).